Radar systems using shaped reflectors to form the beams have been in use for more than 50 years. In such radar systems, a high power transmitter is connected to a port of the reflector antenna, for transmitting a radar beam. Such systems are limited in their antenna beam slew rate by the inertia of the moving reflector, and are not ordinarily capable of modifying the beam shape without modification to the shape of the reflector. Modern radar systems are required to quasi-simultaneously generate plural radar antenna beams pointing in disparate directions, and for this reason tend to use phased-array antennas rather than reflector-type antennas. In a traditional phased-array antenna arrangement, the transmit signal is coupled from a single source or exciter to the individual antenna elements of the array by way of a power dividing beamformer network (beamformer or BFN). The power dividing beamformer applies a small fraction of the excitation energy to each antenna element. Beam steering is accomplished by modularized controllable phase shifters, and sometimes controllable attenuators, associated with the various antenna elements. When high transmitted power is desired, as may be the case when improved signal-to-noise ratio or range is desired, the exciter power can be increased. However, there are physical limitations to the amount of power that can practically or economically be generated. Even if the exciter power is maximized, the beamformer and other parts of the phased-array include lossy elements such as transmission lines, which attenuate the excitation signal. Thus, the power applied to each antenna element in a conventional phased-array antenna is reduced by the “power-dividing” nature of the beamformers, and is also reduced by the presence of unwanted transmission losses.
Active phased-array antennas were developed to adapt to or ameliorate the power-loss aspects of conventional phased-array antennas. In an active phased-array antenna, each antenna element of the antenna array is provided with a transmit-receive (TR) module which includes the controllable phase shifters for beam steering, and also includes its own excitation power amplifier. Low-power excitation is applied through the beamformer to the TR modules of the elements of the antenna array. The low power of the excitation makes it easy to distribute with small transmission paths, and the excitation, when it arrives at the TR module for transmission, is amplified by the excitation power amplifier. A major advantage of the active antenna array is that the high transmitter power is applied to the various TR modules in the form of direct voltage, rather than as a radio-frequency (RF) signal, which reduces the deleterious effects of RF leakage on the operation of the radar or other system using the active array antenna. In the past, the term “radio frequencies” was interpreted to mean a limited range of frequencies, such as, for example, the range extending from about 20 KHz to 2 MHz. Those skilled in the art know that “radio” frequencies as now understood extends over the entire frequency spectrum, including those frequencies in the “microwave” and “millimeter-wave” regions, and up to light-wave frequencies. Many of these frequencies are very important for commercial purposes, as they include the frequencies at which radar systems, global positioning systems, satellite cellular communications and ordinary terrestrial cellphone systems operate.
Since the beam direction of a phased array antenna depends upon the relative amplitudes and phases of the excitation signals applied to the antenna elements, unwanted amplitude and phase errors should desirably be minimized. While distribution of low-power excitation ameliorates unwanted leakage from the exciter to the receiver, the problem remains of causing the beam direction and shape to assume the desired configuration. For this purpose, the phase, and possibly the amplitude characteristics of the various paths are taken into account when setting up such an antenna or radar. The large number of signal paths in a large array antenna makes precalibration of the amplitude and phase of all of the paths difficult and expensive, and the characteristics of the paths may change after they are calibrated due to environmental effects, damage or even simple aging. Various schemes have been put forward for causing desired beam shape and direction control notwithstanding various amplitude and phase defects in the signal transmission paths.
The Counterfire Target Acquisition Radar, Enhanced AN/TPQ-36 operates at various different frequencies, and routes power among various antenna elements of an array by use of a hybrid arrangement. The radar system is precalibrated at each possible operating frequency by adjusting the phase shifts associated with the hybrid in a feedback manner to provide optimal performance, and the calibration values are stored. During normal operation, the calibration values of phase shift are selected and used for feedforward operation at each frequency.
Accurate characterization of the amplitude and phase of the signal or transmission paths (“lines”) in a phased-array antenna requires high isolation in, between and among the various constituent parts of the system. Leakage paths of the characterization signal into unintended signal paths cause errors in the calibration. The smaller the desired calibration inaccuracy, the higher the required isolation.
Some phased-array radar systems, such as the Lockheed Martin Eq36 referred to above, have rigorous specifications which are selected to reduce leakage, and such rigorous specifications tend to drive up the cost of manufacture and may impact on periodic maintenance. FIG. 1 is a highly simplified block diagram 10 of the Eq36 radar system. While the explanation of the invention is directed toward the Eq36 system, the invention may be used wherever corresponding structures are found. In FIG. 1, a transmitter (TX) exciter is illustrated as a block 12. The transmitter exciter has broad capabilities for modulating an excitation signal, and in particular is capable of amplitude modulation (AM), frequency modulation (FM), phase modulation (PM), linear frequency modulation (LFM), and non-linear FM. Exciter block 12, as well as other portions of the radar 10, is controlled by way of a path 15 by a radar control computer (RCC), which is illustrated as a block 14. The controlled excitation from exciter 12 is applied in a transmit mode of operation, by way of a TX path 13, to a monitor feed amplifier (MFA) 18, which is also under control of the RCC 14. The MFA has sensitivity time control (STC) capability, as is common in radar systems for adjusting the receive gain to attenuate signals from close targets, to avoid receiver saturation. In a receive mode of operation, various receive signals are coupled from the monitor feed amplifier 18 to a receiver (RX), illustrated as a block 16. The receiver 16 has a broad instantaneous bandwidth, which can be controlled to virtually any individual frequency and with virtually any desired bandwidth, broad or narrow, within the instantaneous bandwidth. Receiver 16 receives radar receive signals from a monitor feed amplifier (MFA) 18 by way of paths designated together as 17. The various radar receive signals are the upper difference (UΔ), upper sum (UΣ), lower difference (LΔ), lower sum (LΣ), mid difference (MΔ), and mid sum (MΣ), as known in the art. The monitor feed amplifier (MFA) 18 is coupled by way of a beamformer 20 and transmission paths or cables 21 to an active antenna array 22. The active antenna array 22 includes at least phase shifters which are controlled by the radar control computer 14 to direct the electromagnetic radiation 23 of the antenna beams (not illustrated) in both the transmit and receive modes of operation. FIG. 1 also illustrates a “forward” signal flow direction arrow 96 and a “reverse” direction arrow 98.
FIG. 2A illustrates some details 200 of portions of the radar system 10 of FIG. 1. In FIG. 2A, an antenna array designated generally as 216 includes a plurality of arrays of eight antenna elements, together with some ancillary antenna elements. More particularly, the portion of the antenna array 216 illustrated in FIG. 1 includes an array of eight antenna elements designated 216a, another array of eight antenna elements designated 216b, . . . , and a further array of eight antenna elements designated 216h. Antenna array 216 includes some individual antenna elements, one of which is illustrated as 216AUX. Each antenna element of antenna array 216 includes a guided-wave port; the guided-wave ports are designated by the antenna element designation with the suffix “P.” In FIG. 2A, beamformer 20 includes a 1:32 Monitor Feed Divider beamformer portion 236, a 32:2 Mid RX beamformer (BFN)& TX BFN 238, a 32:2 Upper RX BFN, a 32:2 Lower RX BFN 242, together referred to as beamformer portion 235, and a combination 8:3 3 vertical beam Blass network (BLASS is named after an individual) and 4:1 Monitor feed network 250. Also in FIG. 2A, active antenna array 22 includes 32 columns, each column of which includes a plurality of antenna coupling modules of a set of antenna coupling modules 209. Set 209 of antenna coupling modules as illustrated in FIG. 2A includes four “Octapacks” and an auxiliary (AUX) TR (Transmit-Receive) module 210AUX. The four octapacks of a single one of the 32 columns are illustrated in FIG. 2A as 210a, 210b, 210c, and 210d. Each octapack includes eight antenna coupling modules (not illustrated in FIG. 2A), and is connected to an array of eight antenna elements 216. The eight antenna elements to which octapack 210a is connected are designated together as 216a, the eight antenna elements to which octapack 210b is connected are designated together as 216b, the eight antenna elements to which octapack 210c is connected are designated together as 216c, and the eight antenna elements to which octapack 210d is connected are designated together as 216d. Transmit-Receive module 210AUX is connected to a single antenna element 216AUX.
Within beamformer 20 of FIG. 2A, a set of signal paths designated generally as 251 interconnects beamformer portion 235 with beamformer portion 250. More particularly, first signal path 252 of set 251 interconnects combination 8:3 vertical beam Blass network (BLASS) and 4:1 Monitor feed network 250 with 1:32 Monitor Feed Divider network 236. A second signal path 254 interconnects combination 8:3 BLASS network and 4:1 Monitor feed network 250 with 32:2 Mid RX BFN & TX BFN 238. A third signal path 256 interconnects combination 8:3 BLASS network and 4:1 Monitor feed network 250 with 32:2 Lower RX BFN 242. Lastly, a fourth signal path 257 interconnects combination 8:3 BLASS network and 4:1 Monitor feed network 250 with 1:32 Monitor Feed Divider network 236.
In FIG. 2A, various signal paths or lines, designated generally as “RF Cables” 21, connect the beamformer network 20 to the 32 columns, each of eight antenna coupling modules, of the active antenna array 22. Those skilled in the art will understand that the term “cables” should be interpreted as being transmission lines or paths of any sort. Among these transmission paths, some are represented in FIGS. 2A and 3 by dash lines; these are “Monitor Feed Paths”, which are precalibrated as to their amplitude and phase characteristics. The precalibration of only a few of the signal paths (the monitor feed paths) avoids the cost and complexity of initially calibrating all the paths, of which there may be thousands. Once the monitor feed paths are calibrated, the remainder of the signals paths can be calibrated by the method described herein.
FIG. 3 is a simplified representation of the contents of one of the octapacks or 8-TR-module blocks of FIG. 2A, together with the associated set of eight antenna elements. For definiteness, module 210b is represented in FIG. 3, with its array 216b of antenna elements. In FIG. 2A, the three transmission paths which interconnect octapack 210b with combination 8:3 BLASS) network and 4:1 Monitor feed network 250 are 212c, 212d, and 214b. These same transmission paths 212c, 212d, and 214b appear at the left of FIG. 3. Each of transmission paths 212c and 212d is connected to a set of four antenna coupling networks. More particularly, transmission path 212c is connected to a set 310 of antenna coupling networks (ACNs) 310a, 310b, 310c, and 310d. Transmission path 212d is connected to antenna coupling networks 310e, 310f, 310g, and 310h. Antenna coupling network 310a includes a TR module 312a (one of a set 312 of TR modules) which is connected to transmission path 212c, and which is also connected by a pair of conductors to two ports of a circulator 314a. A third port of circulator 314a is connected to a low-pass filter 318a and a sampler or directional coupler 320a of a set 320 of directional couplers. The through path of directional coupler 320a is connected at an antenna port 316baP to a first antenna element 316ba, and the tap port is connected to monitor feed path 214b. The circulators 314a, 314b, . . . of FIG. 3 are part of a set 314 of circulators, the filters 318a, 318b, . . . , are part of a set 318 of circulators, and directional couplers 320a, 320b, . . . , are part of a set 320 of directional couplers.
Similarly, antenna coupling network 310b of FIG. 3 includes a TR module 312b which is connected to transmission path 212c, and which is also connected by a pair of conductors to two ports of a circulator 314b. A third port of circulator 314b is connected to a low-pass filter 318b and a sampler or directional coupler 320b. The through path of directional coupler 320b is connected at an antenna port 316bbP to a second antenna element 316bb. Antenna coupling network 310c of set 310 includes a TR module 312c which is connected to transmission path 212c, and which is also connected by a pair of conductors to two ports of a circulator 314c. A third port of circulator 314c is connected to a low-pass filter 318c and a sampler or directional coupler 320c. The through path of directional coupler 320c is connected at an antenna port 316bcP to a third antenna element 316bc. Antenna coupling network 310d includes a TR module 312d which is connected to transmission path 212c, and which is also connected by a pair of conductors to two ports of a circulator 314d. A third port of circulator 314d is connected to a low-pass filter 318d and a sampler or directional coupler 320d. The through path of directional coupler 320d is connected at an antenna port 316bdP to a further antenna element 316bd. Antenna coupling network 310e includes a TR module 312e which is connected to transmission path 212c, and which is also connected by a pair of conductors to two ports of a circulator 314e. A third port of circulator 314e is connected to a low-pass filter 318e and a sampler or directional coupler 320e. The through path of directional coupler 320e is connected at an antenna port 316beP to a further antenna element 316be. Antenna coupling network 320f includes a TR module 312f which is connected to transmission path 212c, and which is also connected by a pair of conductors to two ports of a circulator 314f. A third port of circulator 314f is connected to a low-pass filter 318f and a sampler or directional coupler 320f. The through path of directional coupler 320f is connected at an antenna port 316bfP to a further antenna element 316bf. Antenna coupling network 310g includes a TR module 312g which is connected to transmission path 212c, and which is also connected by a pair of conductors to two ports of a circulator 314g. A third port of circulator 314g is connected to a low-pass filter 318g and a sampler or directional coupler 320g. The through path of directional coupler 320g is connected at an antenna port 316bgP to a further antenna element 316bg. Antenna coupling network 310h includes a TR module 312h which is connected to transmission path 212c, and which is also connected by a pair of conductors to two ports of a circulator 314h. A third port of circulator 314h is connected to a low-pass filter 318h and a sampler or directional coupler 320h. The through path of directional coupler 320h is connected at an antenna port 316bhP to a further antenna element 316bh. All of the antenna coupling modules of set 310 of FIG. 3 are controlled by RCC 14 by way of path 15.
FIG. 4A is a simplified diagram in schematic and block form, illustrating details of a TR module of FIG. 3, and FIG. 4B illustrates the equivalence of different directional coupler symbols. In FIG. 4A, the particular one of the TR modules is 312c. As illustrated, the interconnection transmission path 212c is connected to an input-output port 412io of a common leg circuit (CLC) block 412. The CLC can apply gain and phase changes in both the transmit and receive modes of operation with the existing EQ36 clock and control signals. In a radar transmit mode of operation, excitation is delivered by way of path 212c and a transmit output port 41201 of CLC 412 to a driver amplifier 414. Amplifier 414, in turn, drives a “high-power amplifier” (HPA) 416, which includes first and second 3 dB splitters or directional couplers 418 and 420 and amplifier portions 416a and 416b. The high-power amplifier can be biased ON and OFF by the radar control computer (RCC) or processor, thereby providing an on-off “switching” function in each forward path. The output of HPA 416 is coupled by a path 430 to a port of circulator 314c of FIG. 3. In a transmit mode of operation, the excitation applied to HPA 416 is amplified and applied by way of circulator 314c (FIG. 3), filter 318c, and directional coupler 320c to the guided-wave port 316bcP of antenna element 316bc for transduction to the form of unguided radiation, which propagates into space. In a receive mode of operation, free-space radiation arrives at the various antenna elements, including antenna element 316bc. That radiation received by antenna element 312bc is transduced to guided-wave form and is applied through directional coupler 320c, filter 318c, circulator 314c, and path 432 to low-noise amplifier (LNA) 422 for amplification. As with the HPA, the LNA can provide an ON/OFF function under the control of the RCC. The amplified received signal is applied through port 412i1 of common leg circuit (CLC) 412 and thence onto transmission path 212c. 
Common leg circuit (CLC) 412 of FIG. 4A includes a single-pole, double-throw switch designated 450 and illustrated as a mechanical switch. As mentioned, those skilled in the art know that such mechanical switches are only symbolic and used for understanding the operation, and that semiconductor or solid-state switches are used instead. The mechanical portions of switch 450 include a common port or terminal 450c, to which one end of a movable element 450m is attached. Movable element 450m can be moved in the directions indicated by a curved, two-headed arrow, so as to contact either a first individual or independent port or terminal 4501 or a second individual port 4502, to thereby provide communication between the common port 450c and the selected one of the individual ports. The state of switch 450, and of other switches in CLC 412, are controlled by way of path 15 by the radar control computer (14 of FIG. 1). Port 4501 of switch 450 of FIG. 4 is connected to an individual port 4521 of a single-pole, double-throw switch 452, and port 4502 is connected by a path 460 to an individual port 4582 of a single-pole, double-throw switch 458. Individual port 4522 of switch 452 is connected by way of path 420 to receive return or reflected signals from low-noise amplifier 412. The common port 452c of switch 452 is connected to a block 454, which includes at least one of amplitude (A) or phase (φ) control, also under the control of RCC 14. The amplitude and phase-controlled signal is applied from block 454 to an amplifier illustrated as 456. The amplified signal from amplifier 456 is applied to the common port 458c of a single-pole, double-throw switch 458. Movable element 458m of switch 458 can contact port 4581 or 4582. Port 4581 is connected to output port 412o1 of CLC 412, and port 4582, as mentioned, is connected to switch 450.
In operation of CLC 412 of FIG. 4, the state of switches 450, 452, and 458 is as illustrated in the transmit mode of operation. During transmission, RF from the exciter arrives at CLC 412 by way of path 212c, and is coupled through switches 450 and 452 and through amplitude and phase control block 454 and amplifier 456 to the common port of switch 458. Switch 458 routes the RF signal by way of driver 414 and high power amplifier 416 to the associated antenna(s) by way of circulator 314c. In a receive mode of operation, the positions of the movable elements of switches 450, 452, and 458 are reversed from that illustrated. During reception, the antenna signals received by the associated antenna(s) are routed by way of circulator 314c and LNA 412 to port 4522 of switch 452, thence through amplitude and phase control block 454 and amplifier 456 to port 4582 of switch 358. From port 4582 of switch 358, the return signals flow by path 460 to port 4502 of switch 452, and by way of movable element 452m to common port 450c. Thus, in the transmit mode the exciter signal is routed by the HPA 416 to the associated antenna element, and in the receive mode the received signal is routed by LNA 422 back to conductor 212c. Conductor 212c ultimately routes the signal to receiver 16 of FIG. 1.
FIG. 5 is a simplified diagram in block and schematic form illustrating details of antenna coupler 210AUX of FIG. 2A. In FIG. 5, antenna coupler 210AUX receives signal from path 213, couples that signal through a TR module 312AUX, which is identical to that of FIG. 4A. In short, the “forward” signal flows through the TR module and through path 530 to a port of a circulator 314AUX. The forward signal is circulated to filter 320AUX and then through directional coupler 520 to an antenna port. In receive mode of operation, the received signal flows through directional coupler 520, filter 320AUX, circulator 314AUX, and through the “reverse” signal path of TR module 312AUX.
Monitor feed amplifier 18 of FIG. 2A also includes a plurality of receive signal amplifiers for amplifying the receive signals from the antenna coupling modules 22. More particularly, a receive amplifier 234a amplifies the AUXiliary signal received from a antenna coupling module 210AUX by way of signal path 213 to produce AUX receive signal for application to the AUX port of receiver 16, a receive amplifier 234c amplifies the receive signal received from a beamformer 238 by way of signal path 239MΣ to produce mid Σ receive signal for application to the MΣ port of receiver 16, a receive amplifier 234d amplifies the receive signal received from beamformer 240 by way of signal path 241UΔ to produce upper Δ receive signal for application to the UΔ port of receiver 16, a receive amplifier 234e amplifies the receive signal received from beamformer 240 by way of signal path 241UΣ to produce upper Σ receive signal for application to the UΣ port of receiver 16, a receive amplifier 234f amplifies the receive signal received from beamformer 242 by way of signal path 243LΔ to produce lower Δ receive signal for application to the LΔ port of receiver 16, and a receive amplifier 234g amplifies the receive signal received from beamformer 242 by way of signal path 243LΣ to produce lower Σ receive signal for application to the LΣ port of receiver 16.
In FIG. 2A, the monitor feed amplifier 18 includes an MFA Switch Arrangement 201, which can take on four operating modes. These modes are transmit and receive in the radar mode and transmit and receive calibration mode, including one for receive and one for transmit. There is also a “loopback” mode or path. MFA switch arrangement 201 is coupled by a monitor feed path 237 to 1:32 Monitor Feed Divider 236, by a paths 239 midΔ and 239t to 32:2 Mid Rx BFN & Tx BFN 238. MFA Switch Arrangement 201 also receives exciter (Tx) signal at MFA port 18i1. FIG. 2B illustrates details of the Monitor Feed Amplifier (MFA) Switch Arrangement 201 of FIG. 2A. FIG. 2B shows the state of the switch arrangement 201 in the receive calibration mode of operation, while FIG. 2C shows the state of the switch arrangement 201 in the transmit calibration mode of operation. In the MFA switch arrangement 201 of FIG. 2B, a directional coupler 224 includes a through path extending from a port 2241 to a port 2242, and has a bidirectional tap port 2243. In MFA switch arrangement 201, the signal from the 239 mid Δ path is applied through a sensitivity time control (STC) gain block 2321 and by way of the through path of directional coupler 224, an amplifier 2291, a second STC gain circuit 2322, and another amplifier 2292 to an individual terminal 2301 of a switch 230. STC is well known in the radar arts, and is used to modulate the gain of the radar system so as to reduce the magnitude of return (clutter) signals from nearby targets. Switch 230 is symbolically illustrated as a mechanical switch, as is conventional for purposes of explanation, but those skilled in the art know that electronic or solid-state switches are used in actual practice. Switch 230 as illustrated includes a common terminal 230c which is coupled by a path 171 to the mid Δ port of receiver 16 of FIG. 1. A movable element 230m is coupled at one end to common port 230c, and the movable end can make contact with either terminal 2301 or 2302. In the illustrated state of switch 230, movable element 230m connects terminal or port 230c to port 2301.
In FIG. 2B, transmit (TX) or exciter signals are applied by way of path 13 and port 18i1 and by way of an exciter signal amplifier including amplifier elements 2201 and 2202 to the common port 221c of a single-pole, double-throw switch 221. Switch 221 includes a movable element 221m which makes continuous contact with common port 221m and can make contact with one or the other of terminals or ports 2211 and 2212. In the position of switch 221 illustrated in FIG. 2B, the exciter signals are routed to a terminal 2262 of a switch 226. In the other position of switch 221, the movable element 221m connects the common terminal 221c to terminal 2212. In such a position, exciter signals flow from switch 221, and through an amplifier 2203 to directional coupler port 2221 of directional coupler 222. Directional coupler 222 routes a portion of the exciter signal by way of the through path to terminal 2222 and path 239t to beamformer portion 238, and another portion to tap port 2223. The portion of the exciter signal leaving tap port 2223 of directional coupler 222 starts on the loopback path, and is routed by way of a high-isolation single-pole single-throw switch 225, illustrated in the nonconnecting or OPEN state, to the tap of a further directional coupler 224. Additionally, in FIG. 2B, switch 226 includes a movable element 226m continuously connected to a common terminal 226c. A further conductor in FIG. 2B connects terminal 2302 of switch 230 to a terminal 2261 of switch 226, and common terminal 226c is connected by conductor 237 to a beamformer portion 236.
FIG. 2C illustrates the MFA Switch 201 of FIG. 2B in the alternative switch condition useful for calibration of the transmit mode.
Calibration of the transmission lines and beamformers in the transmit mode of operation of the prior art arrangement of FIGS. 2A, 2B, 2C, 3, 4A, and 5 is or was performed by injecting an RF signal from the exciter (12 of FIG. 1) into the Transmit port 18i1 of MFA 18 by way of path 13, with the switches of MFA Switch Arrangement 201 set as illustrated in FIG. 2C. The RF signal flows through amplifiers 2201 and 2202, through switch 221 and amplifier 2203, by way of the through path of directional coupler 222 and port 18io to transmission path 239t. The exciter signal coupled onto directional coupler tap port 2223 is blocked from further progress by high isolation switch 225 in its OPEN state. The exciter signal leaving the through path of directional coupler 222 at port 2222 exits the MFA by path 239t of port 18io, then goes through the Tx Beamformer 238, toward the front of the array, and through the 8:3 Blass network 250, into an Octapack, represented by 210b of FIG. 3, and through the CLC, represented by s412 of FIG. 4A, through the HPA 416 of FIG. 4A, the circulator 314C of FIG. 3, the filter of set 314, and is then coupled by way of a directional coupler (of set 320) to a Monitor Feed Path 214 of FIG. 2A (214b in FIG. 3) to start its journey toward the receiver 16 of FIG. 1. There is one monitor feed path for each octapack. The exciter signal returning toward the receiver is applied from a path 214 (path 214b illustrated in FIG. 3) through the 4:1 monitor feed portion of Blass network 250, by way of path 257 into the 1:32 Monitor Feed Divider 236, and by way of path 237 into the MFA Switch Arrangement 201 of MFA 18. Within the MFA Switch Arrangement 201, the exciter signal flows through switch 226 in the state illustrated in FIG. 2C, and through switch 230 and then out the Mid Δ port of the MFA and into the receiver 16. The receiver 16 would then measure the amplitude and phase of the received signal and compare it to the magnitude and phase of the exciter signal that was first sent in preparation for making correction data. As an alternative, the loopback signal path can be enabled, which amounts closing high-isolation switch 225 to apply the exciter signal to the return path. This process would be repeated for all the antenna elements. Then the collected corrected data would be used to correct (via the CLC) each individual element Transmit path to form equal phase and amplitude (or whatever desired beamsteering phase and taper was required at each element).
Similarly, in calibrating the antenna for Receive mode, a known RF signal (magnitude and phase) would be injected into the MFA (by the same port 18i1 as in the case of Transmit calibration mode), however the MFA Switch Arrangement 201 is in the receive state represented by FIG. 2B. The exciter signal flows through amplifiers 2201 and 2202, and by way of switches 221 and 226 to path 237 at port 18io. The exciter signal applied from switch 226 to path 237 flows to the 1:32 Monitor Feed Divider 236, up to the 1:4 250, up to the Octapack by way of a the monitor feed paths such as 214a, 214b, 214c, and 214d, and is coupled over a directional coupler of set 320 of directional couplers, through a filter of set 318 of filters, through a circulator of set 314 of circulators, through the LNA 422 and then the CLC 412, through the 8:3 Blass 250), into the 32:2 Middle Beamformer 238, into the MFA (different port than in Transmit calibration) 18 and then out the MFA MidΔ (same port as Transmit calibration) and finally into the receiver 16. Again the magnitude and phase of this signal would be measured and compared to the magnitude and phase of the signal from the exciter, sampled by way of the loopback path, to prepare for element path Receive mode correction. This would be repeated for the transmission paths related to each antenna element, and the collected corrected magnitude and phases would be applied to the CLC together with the desired magnitude and phases to correct each individual element Receive path to form equal phase and amplitude or whatever desired beamsteering phase and taper was required at each element. It should be noted that the calibration signal need not be transmitted from the antenna array, because the power amplifier 416 can be biased OFF. The LNA 422 can also be biased OFF to prevent amplification of multiple signals in the reverse direction.
Improved radar calibration arrangements and methods are desired.